90 Degree C - Rating

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explorer

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Does anyone know if there is a code provision that prohibits the use of 90 degree conductors in Underground installations. To be more specific can you use the 90 degree column to select the conductor ampacity for an underground installation if you use 90 degree rated terminations and equipment?

John
 

rbalex

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Re: 90 Degree C - Rating

The 90 degree column may be used along with appropriate adjustments from 310.15.

Conductors must be reviewed for ampacity by their conditions of use in each segment of installation and at their terminations as separate evaluations. Different conditions may ultimately be the ruling factor.

More specifically, any derating required in the underground segment for 90C conductors may begin with the 90C column. How they affect other conductors or raceways may also be a consideration.

[ May 21, 2004, 12:09 PM: Message edited by: rbalex ]
 

ryan_618

Senior Member
Re: 90 Degree C - Rating

You would have to use a (-2) conductor or XHHW (310.13, also note 4), and somehow find 90 degree terminations. I have never seen 90 degree terminations, however.
 

ron

Senior Member
Re: 90 Degree C - Rating

The limitation of the terminations in the equipment they bolt to. I have only seen 75 deg max rated equipment, so the 90 deg column is for derating only.
 

stew

Senior Member
Re: 90 Degree C - Rating

As near as I can find there are no devices or terminal blocks that are rated for 90 deg. I had this situation also and spent all kinds of time trying to locate a proper device or terminal and could never find one. So I have to agree the 90 deg is to be used as a starting point for drating only. Dang It !!
 

ron

Senior Member
Re: 90 Degree C - Rating

There are terminations that are rated at 90 degrees all by themselves, but the equipment they get attached to only tests them at 60 or 75 degrees.
For example http://ebusiness.ilsco.com/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&langId=-1&catalogId=1&categoryId=120
When this is terminated in a switchboard, all switchboards that I know of only list it for 75 deg terminations. So you would have to use the 75 deg for ampacity, but you can derate from the 90 deg column.
 

rbalex

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Re: 90 Degree C - Rating

This is taken from the UL General Info Directory for Category Code AALZ Electrical Equipment for Use in Ordinary Locations :
Distribution and Control Equipment Terminations
Most terminals are suitable for use only with copper wire. Where aluminum or copper-clad aluminum wire can or shall be used (some crimp terminals may be Listed only for aluminum wire), there is marking to indicate this. Such marking is required to be independent of any marking on terminal connectors, such as on a wiring diagram or other visible location. The marking may be in an abbreviated form, such as "AL-CU."

Except as noted in the following paragraphs or in the general Guide Information for some product categories, the termination provisions are based on the use of 60?C ampacities for wire size Nos. 14-1 AWG, and 75?C ampacities for wire size Nos. 1/0 AWG and larger, as specified in Table 310.16 of the NEC.

Some distribution and control equipment is marked to indicate the required temperature rating of each field-installed conductor. If the equipment, normally intended for connection by wire sizes within the range 14-1 AWG, is marked "75C" or "60/75C," it is intended that 75?C insulated wire may be used at full 75?C ampacity. Where the connection is made to a circuit breaker or switch within the equipment, such a circuit breaker or switch must also be marked for the temperature rating of the conductor.

A 75?C conductor temperature marking on a circuit breaker or switch normally intended for wire sizes 14-1 AWG does not in itself indicate that 75?C insulated wire can be used unless 1) the circuit breaker or switch is used by itself, such as in a separate enclosure, or 2) the equipment in which the circuit breaker or switch is installed is also so marked.

A 75?C or 90?C temperature marking on a terminal (e.g., AL7, CU7AL, AL7CU or AL9, CU9AL, AL9CU) does not in itself indicate that 75?C or 90?C insulated wire can be used unless the equipment in which the terminals are installed is marked for 75?C or 90?C.

Higher temperature rated conductors than specified may be used if the size is based on the above statements.
BTW nothing is actually listed to this Category Code but virtually everything is evaluated by it.

Generally Medium Voltage equipment uses 90C terminations. There may be a few exceptions - I just don't know of any.

My take on the above quote is that if the equipment is listed for 75C conductors derating at the terminals, if necessary, must also be based on the 75C column.

[ May 21, 2004, 09:46 PM: Message edited by: rbalex ]
 
Re: 90 Degree C - Rating

Explorer said in this case he has 90C conductors, but if he were to use THHN/THWN 90C conductors underground (wet location) you must use the THWN 75C rating.
 
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